Ideal Water Hardness

By: Jake Gallagher | August 22, 2023

You’ve been obsessing over your hard water problems for ages, picturing that pesky water that will clog pipes and damage your hair. But when your neighbors throw around words like “water hardness scale” and “sodium chloride,” you’re too afraid to speak up and reveal what you don’t know. 

You know that dissolved minerals are part of the problem, but you don’t know how that relates to “hard” water. And you sure don’t know how to measure water hardness.

Luckily, you’ve stumbled across this article from your resident expert on water hardness.

Basically, to understand water hardness and thus what the ideal water hardness is for your water supply, compare your plumbing to the human body—specifically the arteries. Those arteries can get clogged. How? Over time, fatty materials and cholesterol stick to the walls of those arteries until they’re blocked. This causes a lot of problems.

Hard water works the same way. Hard water is high in dissolved calcium and magnesium (along with other mineral ions). Like the fats and other unhealthy materials that circulate in your blood, high concentrations of minerals will get stuck and cause an array of problems:

  • mineral buildup in your pipes
  • soap scum on your shower doors
  • dry skin and dry hair after you bathe
  • spotty dishes
  • health problems if you’re drinking hard water

To improve your water quality, you can invest in a water softener. Water softeners remove calcium and magnesium in your water supply to reduce water hardness and prevent some of the uglier effects of hard water. 

The most common type of water softener (the ion exchange system) replaces calcium and magnesium ions with sodium ions. If you’re on a low-sodium diet, consider alternate water softeners. 

Additionally, if you’re worried about the health effects of contaminants in your drinking water, such as chlorine, fluoride, and arsenic, to name just a few, you should look into the best water filter on the market.

Water softeners and filters aside, you need to know what your water hardness should be before you go around trying to install things. In the next few minutes, you’ll learn the difference between soft water and hard water, what the water hardness scale means for your water quality, and how you can fix hard water problems, like mineral buildup.

How Is Water Hardness Measured?

The simple definition of water hardness is the amount of dissolved calcium and magnesium in the water. So when you’re measuring water hardness, you’re actually measuring the amount of calcium carbonate present in the water. 

I know we just talked about naturally occurring minerals like magnesium, so you’re probably wondering how calcium carbonate accounts for all the other minerals floating around in your water supply. According to Kentucky state specialist for aquaculture William A. Wurts, calcium carbonate is more of a stand-in or general term for minerals in water. So water hardness refers to calcium and magnesium levels through calcium carbonate.

Here’s where we get even deeper into the chemistry—units of measurement. There are a few different ways to report the concentration of calcium carbonate. You may see a hardness number in grains per gallon (gpg), parts per million (ppm), or milligrams per liter (mg/L). A hardness number in parts per million just means that one unit of calcium carbonate is dissolved in one million units of water.

The Center for Hazardous Substance Research reports that 1 ppm is approximately 1 mg/L of contaminant in water, so they’re pretty much interchangeable. Also, while all three units show up a lot, gpg is actually the most commonly used measurement.

What Is Considered “Hard” Water?

According to the US Geological Survey, hardness levels are classified by amount of dissolved calcium:

  • Soft: 0–60 mg/L
  • Moderately hard: 61–120 mg/L
  • Hard: 121–180 mg/L
  • Very hard: 180+ mg/L

Since grains per gallon (gpg) is the most common unit of measurement you’ll see when looking at most water softeners or even test kit results, you should probably know the water hardness scale in gpg:

  • Soft: <1 gpg
  • Slightly hard: 1–3.5 gpg
  • Moderately hard: 3.4–7 gpg
  • Hard: 7–10.5 gpg

National data shows that water hardness varies across the United States. So depending on where you live, it’s harder to come by soft water with minimal amounts of dissolved minerals. According to the Geological Survey, water systems using groundwater usually have naturally higher levels of water hardness because water flowing through rock absorbs minerals naturally found in the rock.

As you can see, hardness levels depend on these levels of dissolved minerals, largely calcium and magnesium. While moderately hard water might not be as much of a problem for your hot water heaters, washing machines, and drinking water, hard water leaves spots on your dishes and makes your skin dry.

“Hard” and “very hard” water mean you probably have crusty faucets, pipes, and maybe even reddish rings on your porcelain. You’ll also constantly feel like there’s residue left on your skin after washing your hands and bathing.

The point is, your water’s hardness determines what kind of troubles you’ll find with your tap water and even your drinking water at home.

How Can You Test Water Hardness?

If you think that only professionals can test your water and tell you whether it meets acceptable levels of hardness, think again.

You can buy your own test kit and use it at home. The inorganic chemical test, or Kit C, can be ordered from the Health Department Laboratory and used at home. If you’re a private well owner, you should be doing this every five years. Another option is to bottle up some of your water and send it to a certified drinking water lab.

Other than that, there are water hardness titration kits and easy-to-use test strips. Both types of kits test for hardness using color change to show the presence and severity of hard water. See? Testing your water’s hardness can be as easy as dipping a couple of test strips in a sample of your water.

Whether you purchase a test kit or send some bottles over to a certified drinking water lab, your test results require a bit of water hardness knowledge. Luckily, now you know the water hardness scale in both grains per gallon (gpg) and milligrams per liter (mg/L), which is basically the same as parts per million (ppm).

The point is, you are perfectly capable of determining just how hard your hard water is.

What’s the Ideal Water Hardness?

And now for what you’ve all been waiting for—the perfect level of water hardness. The answer might be a little anticlimactic, but it’s the truth.

There isn’t a perfect level of water hardness.

That being said, there is a range you’ll want to fall within so that you aren’t dealing with soap scum and other negative effects of hard water. Ultimately, if you’re dealing with hard water, your water quality is highly dependent on your water softener. So let’s look at what the water softener companies recommend.

Over at Water Pursuit, water treatment specialists refer to the Department of Health’s rule of thumb— water above 7 gpg or 120 mg/L is too hard. At that point, you’ll want to look into water softener options.

Another general rule for telling whether your water is too hard is by seeing how soap reacts with it on a daily basis. Soap reacts with calcium, which we know is way higher in hard water than in soft water. Thanks to that reaction, more soap and detergent is needed to get things clean. So if you notice that you’re using more soap than usual to clean your laundry or wash your hands, your water hardness levels are not ideal for your household.

If you’re worried about drinking water that isn’t exactly crystal clear, you aren’t alone. But according to the Vermont Department of Health, hard water itself is not a health risk. The calcium and magnesium even contribute positively to your overall mineral intake—even if you aren’t too keen on drinking murky hard water.

Actually, drinking soft water is more of a health risk. Like I mentioned earlier, most water softeners use an ion exchange system. That means minerals are removed, but sodium is then released into your drinking water. If you are at risk of hypertension or simply don’t want a high-sodium diet, soft water might be a health risk for you!


By now, you’re practically a chemist. All that talk about test kits and parts per million wasn’t for nothing! 

You now know that not everything you hear about hard water is true. When most people think of the minerals floating around in their water supply, they’re afraid of the health risks, but you know that humans need calcium and magnesium to stay healthy and water softeners might pose even more of a health risk.

You know there isn’t an ideal water hardness, no exact number your water supply should be at. But a good rule of thumb is that anything above 7 gpg or 120 mg/L is too hard, meaning that you’ll start to see scum in your shower and on your dishes, and you’ll feel it on your skin.

Finally, you know that you can test the hardness of your water on your own with take-home test kits or lab kits. That’s right—no professionals needed! You can handle all those color changing strips and samples on your own.

And with that, you’ve got everything you need to figure out whether you need a water softener!